Superficially a social problem-play about caring for elderly, George Rubino's "The Last Tennant," an ABC Theater presentation on Channel 7 Sunday at 9 p.m., dabbles in enough nuances of human behavior so as to remain a story of people and not of issues or statistics.

Unfortunately, the drama - directed by Jud Taylor - hasn't enough momentum in its second hour to hold a viewers attention, and Rubino wanders off into too many tangential aspects of his basic situation. This makes the play frustrating but hardly worthless; compared to most of ABC's prime-time fare, it is utterly O'Neill.

Lee Strasberg, the famous acting teacher and a star of "The God-father, Part Two," plays a 76-year-old man living alone in New York and clinging to the only one of his children who will still visit and look after him, 36-year-old Joey, played by Tony LoBianco.

Papa has bouts of foregetfulness, but isn't senile. Yet he becomes a burden to his children and a dilemma for Joey, who wants to get married but fears abandoning the old man. Rubino examines this crisis from every angle and sometimes scores victories of truth, but he keeps adding new wrinkles that tend to confuse the story rather than flesh it out.

Late in the film, for instance, we hear from the old man's children that he wasn't much of a father; that he could be tyrannical and unfeeling. The accusations and breast beatings get hot and heavy-handed and at times it seems we're trapped in a play Arthur Miller might have written 20 years ago.

The performers do their utmost to put this over, however, and the most affecting of them may be Christine Lahti as Carol, the woman Joey wants to marry. The way she expresses her concerns and misgivings - Joey considers inviting Papa to come and live with the newlyweds - is really the most convincing voice in the chorus of guilt.

Rubino won a $10,000 price from ABC, in competition with other young writers, for "The Last Tenant," his first work to be produced for television. It can't be said from the evidence that a major talent has been uncovered, but Rubino has the capacity for dealing intelligently with common human predicaments and such nearly universal fears as that of finding oneself with nothing to say to one's parents. There should be many people like Rubino writing dramas like this for network TV. There aren't.